Urban Household Transmission of SARS-CoV-2 During Periods of High and Low Community Transmission

Abstract

Background: Household transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) significantly contributes to increased community cases. Methods: We conducted a prospective case-ascertained study to investigate the household secondary attack rate (SAR) and contributing factors in urban Los Angeles, California, USA. Household members were enrolled prospectively if ≥1 member tested positive for SARS-CoV-2 by polymerase chain reaction (PCR). Nasopharyngeal swabs for PCR and symptom data were obtained over multiple longitudinal visits. Serology was obtained at enrollment. Findings: A total of 489 individuals in 105 households were enrolled from June to December 2020. The mean household SAR was 77.7% (95%CI: 71.4-84.0). A third (32.1%) of index cases were asymptomatic. High SAR was associated with both symptomatic and asymptomatic index cases (76.4% [95%CI: 68.8-83.9%] vs. 79.7% [95% CI: 66.2-93.3%], p=0.66). The most common age for index cases was children Children and adults index cases both efficiently transmitted SARS-CoV-2 within households (SAR 74.0% [95%CI: 63.4-84.6%] vs. 81.3% [95%CI: 72.3-90.3%], p=0.49). Hispanic/Latinx ethnicity was significantly associated with higher SAR in the multivariable analysis of household factors (p= 0.030). Interpretation: The SAR in our urban setting with large ethnic minority populations is much higher than previously described. SAR was disproportionately and significantly impacted by Hispanic/Latinx ethnicity. Asymptomatic individuals and children play important roles as index cases. Future vaccination and public health efforts need special focus on these groups to help mitigate SARS-CoV-2 spread.Funding: NIH/NIAID U01AI144616-02S1, Open PhilanthropyDeclaration of Interests: PSP has received consultant fees from Sanofi-Pasteur and Seqirus. She also receives research funding from AstraZeneca for an unrelated study. AG has received consultant fees from Janssen. All other authors have no conflicts of interest to report.Ethics Approval Statement: The study was approved by the Institutional Review Board at Children’sHospital Los Angeles.